Burners For Liquid Or Gaseous Fuels

Abstract

This invention relates to a burner for liquid or gaseous fuels composed of hree coaxial ducts, the intermediate duct and the outer duct defining an annular space for distributing the combustion-supporting air, which burner comprises fins placed in said annular space, behind the nozzle of the burner, and means forming a perforated screen, placed in said intermediate space, downstream of the fins, so that an eddy of burning fluid is formed about the nozzle of the burner.

Description

The present invention relates to burners for liquid or gaseous fuels.

It is known that the burners of liquid fuels provided in industrial boilers or furnaces generally comprise a central duct, or injection nozzle, for distributing the fuel under pressure, terminating at its end, on the furnace side, by at atomising nozzle. This nozzle projects the droplets of liquid fuel in divergent directions, whose envelope is substantially a cone of revolution about the axis of the burner.

In the case of gaseous fuels, it is substantially the same case, and only the way in which the fuel is projected in order to constitute the jets which are mixed with the combustion-supporting air, varies.

The combustion-supporting air is distributed in a cylindrical duct of larger diameter, coaxial with the injection nozzle.

The air may be divided into two parts, the primary air distributed in an intermediate duct and the secondary air distributed in an outer duct. The secondary air may or may not be animated by a rotary movement about the axis of the burner by means of fins disposed in the secondary air duct. About the nozzle of the burner, eddies of air tend to be formed which are animated by a high speed of rotation, these air eddies being located between the cone of projection of fuel and the central layers of combustion-supporting air. The centrifugal force due to this speed tends to project droplets of liquid fuel laterally or to drive part of the gaseous fuel outwardly which pass through the layers of combustion-supporting air without completely burning. This results in a poor combustion which produces smoke and soot.

The author of the present invention has noted that these eddies could be beneficial on condition that they are ignited. Experience has shown that the clinging of the flame to the nozzle of the burner and the quality of the combustion and ignition are clearly bettwe when a toric eddy is created about the nozzle of the burner, extending in part to the rear of the nozzle of the burner, formed of a mixture of fuel and combustion-supporting air taken from the two currents which enframe said eddy and when this eddy is supplied with combustion-supporting air in order to maintain it burning without the supply of combustion-supporting air being too intense and risking eliminating said eddy by blowing it out.

It is therefore an object of the invention to create an eddy of burning fluid around the nozzle of the burner.

This aim is attained by disposing fins in the secondary combustion air duct which are recessed with respect to the nozzle of the burner and by placing, downstream of said fins a perforated screen under whose shelter a zone of depression is formed in which an eddy of burning fluid is created.

The result of the formation of this eddy is a better combustion enabling the excess of air to be reduced to a maximum, this diminishing the smoke and reducing the risks of formation of sulphuric acid from the usual fuels containing sulphur.

In a particular embodiment, the burner comprises three coaxial ducts : a central duct for distributing the fuel, an intermediate duct for distributing the primary combustion-supporting air and an outer duct for distributing the secondary combustion-supporting air and the fins are fixed to the periphery of a hub surrounding the intermediate duct, the diameter of which is substantially equal to half the diameter of the outer conduit, which hub is pierced with channels of small diameter which transverse is right through in order to supply the eddy with combustion air.

These channels may be parallel to the axis or converging towards the front. In this case, it is the hub which fulfills the function of screen.

The diameter of the perforations or of the channels feeding the eddy with combustion air must be small and determined with accuracy in order not to destroy the depression behind the screen.

The fins are preferably curved, their upstream edge being parallel to the axis and the downsteam edge forming with the axis an angle which decreases from the centre up to the periphery where it becomes parallel to the axis.

Thanks to this arrangement, the layers of combustion-supporting air located near the centre have a higher tangential speed, this causing turbulences and facilitating the formation of the eddy.

Cylindrical deflectors, coaxial with the burner, may be placed between the fins. These deflectors divide the secondary combustion-supporting air into separate layers, this reducing the interactions between layers which cause disturbances in the flow of the secondary combustion-supporting air, which would risk destroying the eddy of burning fluid.

In a particular embodiment of the invention, the fins are fixed to the inner wall of the outer duct and the perforated disc forming the screen is fixed to the intermediate duct, substantially in the same plane perpendicular to the axis. The outer duct and the intermediate duct are movable with respect to each other so that the relative position of the fins and the screen can be slightly modified, by trial and error, in order to look for the position which gives the eddy the most extensive and most stable position.

In combination with the perforated screen, under whose shelter the eddy is formed, air deflectors are preferably used, placed upstream of the fins, which are sectioned longitudinally in order to pipe the air upstream of the fins and to quieten the flow, whilst avoiding the parasitic turbulences.

In the frequent case of the burner comprising a valve sliding opposite the air inlet located in the lateral wall of the outer duct in order to regulate the surfaces of this opening and the outflow of combustion-supporting air, one of the deflectors, located inside the outer duct, is integral with said valve on which is is perpendicularly connected all around said opening.

The burner according to the invention differs from the known turbulence devices, for example : -- the deflector disc provided with a central aperture -- the conical flame deflectors -- the flame boxes.

These known devices have a different aim. They create a zone of turbulence about the flame or inside the flame but none of them enables an eddy of burning fluid to be obtained, located in part to the rear of the nozzle of the burner. The means used are also different, none of these devices comprising, to the rear of the nozzle of the burner, a screen under whose shelter a zone of depression is formed.

Devices exist which comprise, in the duct distributing combustion-supporting air, a "rosette" with fins fixed to a hub. However, this hub fulfills the exclusive mechanical role of support for the fins. It is not large enough to form a screen and it does not comprise channels passing right through.

The accompanying drawings illustrate, by way of example, embodiments of devices in accordance with the invention which are described hereinafter.

FIG. 1 is a longitudinal section of a device according to the invention.

FIG. 2 is a transverse section along III--III of FIG. 1.

FIG. 3 is a longitudinal section through a rosette equipping another device according to the invention.

FIG. 4 is a longitudinal section of another device according to the invention.

FIG. 5 is a longitudinal section through another device comprising a gaseous fuel distribution.

FIG. 6 is a longitudinal section through a device comprising combustion air deflectors upstream of the rosette.

Referring now to the drawings, FIG. 1 shows a duct 1 for distributing fuel, terminated by a nozzle 2. The duct 1 is disposed along axis x--x' of a tube 3 terminated by a conical nozzle 4. On the outer periphery of the tube 3 and recessed with respect to the nozzle, there is disposed a large solid cylindrical hub 5 carrying on its periphery radial fins 6 forming a rosette whose axis is merged with the axis x--x'. The whole is placed inside a cylindrical air distributor duct 7 which may or may not be widened at its front end. The fins 6 occupy a large part of the space between the hub 5 and the duct 7.

The fuel is projected in diverging directions, whose envelope is constituted by the cone of revolution 8. The combustion-supporting air arrives in duct 7 at a longitudinal velocity in the direction of arrows A. The fins 6 are inclined on axis x--x' so that on leaving the fins, the combustion-supporting air is animated by a speed having a transverse component which is constant or variable according to the radius. The air layers, on leaving the rosette, form concentric hyperboloids.

A zone of depression is thus constituted under shelter of the hub which forms a screen. In this zone there is formed an eddy 10 revolving about the axis x--x'. This eddy causes particles of fuel or incompletely burnt gases to be driven upstream. The combustion continues in the eddy which is ignited due to the air driven peripherally or by injection through the hub.

FIG. 2 shows the device of FIG. 1 in transverse section. The fins of this divice have an entry surface whose tangential plane is substantially parallel to the axis x--x' whilst the downstream edge is inclined on the axis x--x'. The inclination of the downsteam edge decreased from the centre to the periphery so that the rotation of the layers of air near the centre is stronger than that of the layers located on the periphery.

As a variant, the fins may be flat or with curvilinear section and of width decreasing from the centre to the periphery in order that, as before, the central layers of air have a greater speed of rotation, this favouring the formation of the central eddy of the flame and of the toric eddy.

In order to supply the eddy of burning fluid with combustion air, small holes 15 which are parallel to the axis x--x' or inclined with respect thereto in one or two directions, may be pierced through the hub 5.

The zone of the eddy is particularly favourable for placing therein the devices for igniting the flame, such as electrodes generating electric sparks or pilot light.

FIG. 3 shows another embodiment in which like elements are designated by the same reference numerals. This device differs from the preceding one in that it comprises, between the fins 6 of the rosette, circular deflectors 11a, 11b, for piping the air and separating the layers of combustion-supporting air into several elementary hyperboloids.

FIG. 4 shows another embodiment in longitudinal section.

The elements similar to those of the preceding Figures are designated by the same reference numbers. This FIG. shows the whole of the device including the valve for the inlet of combustion-supporting air which penetrates into the cylindrical conduit 7 in the direction of arrows 12, through a peripheral opening.

The outflow of combustion-supporting air may be regulated by adjusting the width of the opening by means of a sliding valve 13 actuated by the manoeuvring key 14.

In this embodiment, the fins 6, which constitute the rosette, are fixed to the duct 7 by means of the radial centering fins 16 and are independent of the hub 5 which is fixed to the duct 3. This arrangement enables the relative position of the nozzle of the burner to be varied with respect to the rosette in order to find the one which corresponds to the best combustion.

FIG. 5 shows an embodiment comprising a burner that may be a mixed burner with liquid or gaseous fuel or a solely gas burner. The arrangement of the rosette and the hub remains identical to that of the previous Figure. The combustion air duct 7 comprises a double wall 7a, 7b and the intermediate space serves as a duct for distributing fuel gas which is injected through apertures 17 which may or may not be provided with elongated nozzles placed in front of the rosette 6 either perpendicularly to the wall, inclined forwardly, or inclined rearwardly in order that part of the jets of gas supplies the toric eddy 10 in order for it to remain burning, as in the previous cases.

FIG. 6 shows another embodiment, like elements being designated by like reference numerals. The combustion air penetrates radially in the direction of arrows 12 into duct 7. The sliding valve 13 enables the outflow of air to be regulated. Longitudinally sectioned deflectors pipe the combustion air from the radial direction to the rosette 6, so that the flow of air remains laminar. These deflectors are composed of a surface 18 revolving about axis x--x', which is fixed to the rear wall of the device and of another surface 19 revolving about x--x', fixed to the sliding valve.

The deflector possibly comprises, in addition, a cone of revolution 20 upstream of the hub 5, which pipes the streams of air up to the fins of the rosette.

The longitudinal sections of the surfaces 18 and 19 are obviously studied to eliminate the formation of any parasitic eddy along the walls.

The combination of the deflectors 18, 19 and possibly 20 with a rosette 6 and a hub 5 forming a screen and clearly recessed with respect to the nozzle of the burner results in the formation of a very regular eddy 10 of burning fluid, with a very stable flame.

Claims

What is claimed is:

1. Burner of liquid or gaseous fuels composed of three coaxial cylindrical ducts: a central duct, of small diameter, for distributing the fuel, terminated by a nozzle forming the nozzle of the burner; an intermediate duct, of slightly larger diameter, for distributing the primary combustion-supporting air, terminated by a nozzle at its end adjacent said first-mentioned nozzle and an outer duct, of larger diameter than said intermediate duct, defining with said intermediate duct an annular space in which the secondary combustion-supporting air circulates, said burner comprising in addition fins which occupy the larger part of said annular space, and which are recessed with respect to said end of said intermediate duct and means forming a perforated screen disposed on the periphery of said intermediate duct, downstream of said fins, so that there is formed, under the shelter of said screen and around said end of said intermediate duct, an eddy of burning fluid which extends in part upstread of said first-mentioned nozzle.

2. Burner as claimed in claim 1, in which said screen means are constituted by a disc, placed on the periphery of said intermediate duct, the outer diameter of which is substantially equal to the one half the diameter of said outer duct, which disc comprises channels of small diameter passing right through it, said channels supplying the eddy of burning fluid with combustion air without blowing it out.

3. Burner as claimed in claim 2, in which said disc is constituted by a hub carrying said fins on its periphery, through which are pierced channels parallel to the axis of the burner.

4. Burner as claimed in claim 2 in which said disc is constituted by a hub carrying said fins on its periphery, through which are pierced channels inclined with respect to the axis and converging forwardly.

5. Burner as claimed in claim 1, in which the fins are curved, their upstream edge is parallel to the axis and their downstream edge forms with the axis of the burner an angle which decreases from the hub to the periphery of the fins where the downstream edge is parallel to the axis.

6. Burner as claimed in claim 1, in which the cylindrical and coaxial air deflectors are disposed between said fins.

7. Burner as claimed in claim 2, in which said fins are fixed to the inner wall of said outer duct and are independent of said disc which is fixed to the periphery of said intermediate duct and said intermediate and outer ducts are movable longitudinally with respect to one another so that the relative position of the disc and the fins may be modified.

8. Burner as claimed in claim 3 in which said outer conduit comprises, to the rear, a lateral combustion air inlet opening, which burner comprises, in addition, a cylindrical air valve sliding about said outer duct in order to regulate the surface of said opening and a longitudinally sectioned air deflector located inside said outer duct, downstream of said air inlet opening, which deflector is integral with said sliding valve.

9. Burner as claimed in claim 8, wherein said deflector is connected to said valve by its upstream end which is normally connected to the wall of said valve about the end of said valve which defines the air inlet opening and the downstream end of said deflector is parallel to the inner wall of said outer duct against which it slides.

10. Burner as claimed in claim 9, comprising, in addition, a second fixed deflector located inside said annular space, in the rear part thereof, the section of which is substantially parallel to that of the movable deflector and a third fixed truncated deflector placed upstream of said hub, the diameter of the upstream end of which is slightly larger than the outer diameter of said intermediate tube and the diameter of the downstream end of which is substantially equal to the outer diameter of said hub.